In Release7, 3GPP (3rd Generation Partnership Project) adopts technologies of orthogonal frequency division multiplexing (abbreviated as OFDM) and multiple-input multiple-output (abbreviated as MIMO) to complete a future evolved path HSPA+ of HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access). HSPA+ is an enhanced technology of 3GPP HSPA (including HSDPA and HSUPA), which provides an approach of smoothly evolving from HSPA to LTE with low complexity and low cost for HSPA operator.
HSPA+ enhances peak data rate and spectrum efficiency by adopting technologies such as a high order modulation (such as downlink 64QAM (Quadrature Amplitude Modulation) and uplink 16QAM), a MIMO and the combination of high order modulation and MIMO, etc. On the other hand, in order to better support packet services, HSPA+ also adopts a series of other enhanced technologies to achieve the objects of increasing user capacity, reducing time delay, reducing electricity consumption of the terminal, better supporting the voice over IP communication (VOIP) and enhancing multicast/broadcast abilities of the system, etc.
Compared with HSPA, HSPA+ devolves functions of a radio network controller (abbreviated as RNC) to a base station node B (Node B) on a system architecture, to form a completely flattened radio access network architecture, as shown in FIG. 1. At the moment, the Node B integrated with the complete RNC functions is referred to as an Evolved HSPA Node B or abbreviated as enhanced Node B (Node B+). SGSN+ is the SGSN (SERVICE GPRS (General Packet Radio System) SUPPORT NODE) which is upgraded to be able to support the HSPA+ functions. ME+ is a user terminal equipment which can support the HSPA+ functions (also referred to as UE+). The evolved HSPA system can employ 3GPP Rel-5 and the later air interface version without any modification to the HSPA services of the air interface. After adopting this solution, each Node B+ becomes a node equivalent to RNC and has an Iu-PS interface which can be directly connected with a PS CN (Core Network); an Iu-PS user plane terminates in the SGSN; wherein, if the network supports the direct tunnel function, the Iu-PS user plane can also terminate in a GGSN (Gateway GPRS Support Node). The communication between the evolved HSPA Nodes B is performed via an Iur interface. The Node B+ has independent networking ability and supports the whole mobility function, including inter-system and intra-system handover.
In the HSPA+, Node B+ can be viewed as a combination of Node B and RNC. Both of them are one physical entity, but they are still 2 different logic entities. Therefore, herein, the Node B+ which supports a HSPA+ enhanced key hierarchy can also be equivalent to the upgraded RNC in the UMTS. For the sake of distinguishing, it can be referred to as RNC+.
The structure of the currently proposed HSPA+ enhanced security key hierarchy is shown in FIG. 2. Definitions of K (Key, i.e., root key), CK (Ciphering key) and IK (Integrity key) are completely consistent with those in UMTS (Universal Mobile Telecommunications System). That is, K is a root key stored in an AuC (Authentication Center) and a USIM (UNIVERSAL SUBSCRIBER IDENTITY MODULE), CK and IK are the ciphering key and the integrity key calculated by K when the user equipment carries out an AKA (Authentication and Key Agreement) with an HSS. In the UMTS, the RNC uses CK and IK to carry out ciphering and integrity protection on the data. CK and IK can be referred to as conventional air interface security keys, abbreviated as conventional keys.
Since in the HSPA+ architecture, all the functions of the RNC are devolved to the base station Node B+, then the deciphering and ciphering need to be carried out in the Node B+; but the Node B+ is located in an insecure environment, and the security is not particularly high. Therefore, the HSPA+ introduces a key hierarchy similar to EUTRAN (Evolved Universal Terrestrial Radio Access Network), i.e., UTRAN key hierarchy. In the UTRAN key hierarchy structure, the intermediate key KRNC (also referred to as KASMEU sometimes) is a key newly introduced by HSPA+ and generated by deducing from the conventional keys CK and IK. Further, KRNC generates CKU (also referred to as CKS) and IKU (also referred to as IKS), wherein, CKU is used for ciphering user plane data and control plane signalings, and IKU is used for carrying out the integrity protection to the control plane signalings. CKU and IKU are referred to as enhanced air interface security keys, abbreviated as enhanced keys.
LTE/SAE is an evolved technology for UMTS by 3GPP, which supports to provide the peak rate of downlink 100 Mbps and uplink 50 Mbps under the 20 MHz spectrum bandwidth. The network of LTE/SAE consists of a user equipment (UE), an access network and a core network. The whole LTR architecture is shown in FIG. 3. In the EUTRA, the base station equipment is an evolved Node-B (abbreviated as eNB), which is mainly responsible for wireless communication, wireless communication management and mobility context management. The core network includes a mobility management entity (abbreviated as MME), and the MME is responsible for control plane related works such as managing of the mobility management, processing of non-access stratum signaling, and managing of user security mode, etc.
When the user moves from the EUTRAN to the UTRAN, the source MME generates mapped traditional keys IK′ and CK′ according to the key KASME in the LTE, and the deduction formula of the mapped traditional keys are as follows:IK′∥CK′=KDF(KASME,downlink NAS COUNT),
wherein, KDF is a security algorithm defined by 3GPP, and its specific definition can make reference to 3GPP related specifications. KASME is the key generated according to CK by the HSS, and is issued to the MME in the process of the AKA (Authentication and Key Agreement), for deducing the NAS (non-access stratum) key and AS (access stratum) key on the eNB. NAS COUNT is an NAS counter, and each EPS NAS security context is associated with 2 NAS COUNTs: one is an uplink NAS COUNT and the other is a downlink NAS COUNT. The length of the NAS COUNT is 24 bits, and is maintained by the UE and the MME independently. When the AKA runs successfully once and a new KASME is generated, the NAS COUNT is initialized as 0.
The source MME sends the mapped traditional keys IK′ and CK′ which are obtained by deducing to the core network node SGSN of the target network. The target SGSN employs these mapped traditional keys to protect the communication between the user and the network.
With the introduction of HSPA+ security, due to the addition of key hierarchy, the enhanced keys IKU and CKU are employed between the user and the network to protect the communication therebetween. When the user moves from the EUTRAN to the UTRAN which supports the HSPA+ security function, how to establish the enhanced security keys of the HSPA+ via the mapped traditional keys is a problem to be solved.